﻿using System.Collections.Generic;

namespace DataStructures.UnrolledList
{
    /// <summary>
    /// Unrolled linked list is a linked list of small arrays,
    /// all of the same size where each is so small that the insertion
    /// or deletion is fast and quick, but large enough to fill the cache line.
    /// </summary>
    public class UnrolledLinkedList
    {
        private readonly int sizeNode;

        private UnrolledLinkedListNode start = null!;
        private UnrolledLinkedListNode end = null!;

        /// <summary>
        /// Initializes a new instance of the <see cref="UnrolledLinkedList"/> class.
        /// Create a unrolled list with start chunk size.
        /// </summary>
        /// <param name="chunkSize">The size of signe chunk.</param>
        public UnrolledLinkedList(int chunkSize)
        {
            sizeNode = chunkSize + 1;
        }

        /// <summary>
        /// Add value to list [O(n)].
        /// </summary>
        /// <param name="value">The entered value.</param>
        public void Insert(int value)
        {
            if (start == null)
            {
                start = new UnrolledLinkedListNode(sizeNode);
                start.Set(0, value);

                end = start;
                return;
            }

            if (end.Count + 1 < sizeNode)
            {
                end.Set(end.Count, value);
            }
            else
            {
                var pointer = new UnrolledLinkedListNode(sizeNode);
                var j = 0;
                for (var pos = end.Count / 2 + 1; pos < end.Count; pos++)
                {
                    pointer.Set(j++, end.Get(pos));
                }

                pointer.Set(j++, value);
                pointer.Count = j;

                end.Count = end.Count / 2 + 1;
                end.Next = pointer;
                end = pointer;
            }
        }

        /// <summary>
        /// Help method. Get all list inside to check the state.
        /// </summary>
        /// <returns>Items from all nodes.</returns>
        public IEnumerable<int> GetRolledItems()
        {
            UnrolledLinkedListNode pointer = start;
            List<int> result = new();

            while (pointer != null)
            {
                for (var i = 0; i < pointer.Count; i++)
                {
                    result.Add(pointer.Get(i));
                }

                pointer = pointer.Next;
            }

            return result;
        }
    }
}
